A discharge ionization detector operates by applying a high voltage across discharge electrodes that are located in a gas-filled discharge chamber. In the presence of helium, a characteristic discharge emission of photons occurs. The photons irradiate a port connecting the discharge chamber to an ionization chamber receiving a sample gas that contains an unknown component. Electrons are produced in the ionization chamber as a result of photon interaction with ionizable molecules in the column effluent. Helium metastables are also generated in the discharge chamber and are found to play a role in ionization of the analyte of interest. The magnitude of the ionized analytes is manifested as a current that can be measured to ascertain the composition of one or more components in the analyte.
Discharge ionization detectors are disclosed in U.S. Pat. Nos. 4,789,783; 4,975,648; and 5,153,519. As disclosed in U.S. Pat. No. 4,975,648, the geometry of the two chambers and of the emitter/collector electrodes in the detector are said to be important to the efficient operation of the detector, and the collector and emitter electrodes are said to be shaped and positioned relative to the inlet for the sample gas and to the aperture (inlet) from the discharge chamber into the ionization chamber so that improved sensitivity will result. The relative size of the chambers, a smaller ionization chamber in particular, is also described as being important for detector sensitivity.
Although the design of discharge ionization detectors continues to be an object of study in the prior art, there nonetheless exists a need for a discharge ionization detector having a detector response that exhibits an improved dynamic range, lower minimum detectable level (MDL), and greater signal to noise ratio.